Sealing device and sealing method

ABSTRACT

A sealing apparatus and a method for sealing, which make possible reduced installation space and assembly at room temperature, are proposed. The sealing apparatus encompasses a ceramic base element and a metallic housing. The ceramic base element comprises on an outer wall at least one circumferential flute in the region of which the housing is pressed in positively fitting fashion onto the ceramic base element.

FIELD OF THE INVENTION

The present invention is based on a sealing apparatus, and from a methodfor sealing.

BACKGROUND INFORMATION

In order to ensure the functionality of, for example, a spark plug,engine gases must not escape between a spark plug housing and a ceramicinsulator of the spark plug. The ceramic insulator must be installedsealedly into the spark plug housing in such a way that gas-tightness isguaranteed at up to 20 bar, at a maximum temperature of 220° C.

Known for this purpose, for example, is hot assembly, in which the sparkplug housing, after introduction of the ceramic insulator, is heated toapproximately 950° C. in the region of a shrinkage zone. During this,the spark plug housing is pressed onto the ceramic insulator by appliedforces. Upon cooling of the shrinkage zone, tensile stresses areproduced in the spark plug housing with respect to the ceramicinsulator. The applied forces are then removed. The ceramic insulator isthereby sealed in gas-tight fashion with respect to the spark plughousing.

A further method for gas-tight sealing of the ceramic insulator withrespect to the spark plug housing is achieved by way of a cold assemblymethod with powder sealing. Here the ceramic insulator, together with afine ceramic powder, is pushed under load into the spark plug housing.The upper rim of the spark plug housing, through which the ceramicinsulator was introduced into the spark plug housing, is then clinchedover by axial forces in a crimping process, so that the spark plughousing abuts, at its upper rim as well, against the ceramic insulatorand holds the latter in the spark plug housing in gas-tight and sealingfashion.

SUMMARY OF THE INVENTION

The sealing apparatus and method for sealing according to the presentinvention having the features of the independent claims have, incontrast, the advantage that the ceramic base element comprises on anouter wall at least one circumferential flute in the region of which thehousing is pressed in positively fitting fashion onto the ceramic baseelement. This makes possible assembly of the sealing apparatus at roomtemperature. As a result, all common corrosion protection coatings, forexample zinc, transparent chromating, or corrosion protection lacquer,can be applied onto the metallic housing prior to assembly of thesealing apparatus. Furthermore, it is not necessary for the ceramic baseelement to have a shoulder in the region of the upper rim of the housingthrough which the ceramic base element is introduced into the housing,as is the case, for example, with spark plugs in order to receive acrimping of the upper rim of the housing. To the contrary, the gas-tightseal is ensured solely by the pressing of the housing onto the ceramicbase element in the region of the at least one flute. Because theaforesaid shoulder is omitted, the ceramic base element can beimplemented with a smaller cross-sectional area and thus with a smallerdiameter. This is advantageous in particular for use of the sealingapparatus in a spark plug, a sheathed-element glow plug, or a lambdasensor, since space in the cylinder head or in the exhaust system isthus saved and is therefore available for other components, for exampleinjection valves or cooling channels.

It is advantageous if the ceramic base element is at least partiallysolder-joined to the housing. The gas-tightness of the sealing apparatuscan be even further enhanced in this fashion.

A particularly simple method for sealing the ceramic base element in themetallic housing results when the ceramic base element, in the contextof a mechanical reshaping method, in a first step is introduced into thehousing substantially coaxially with the housing, and when in the secondstep a reduction or drawing ring is placed on an outer boundary of thehousing and is pushed in the radial direction into at least one flute,in order to press the housing sealingly onto the ceramic base element inthe region of the at least one flute. This process requires littleoutlay in terms of assembly and tools.

It is furthermore advantageous if the reduction or drawing ring is alsopushed tangentially with respect to the at least one flute against theouter edge of the housing, while the ceramic base element is held in thehousing against the tangential force. In this fashion the housing ispressed, in the region of the at least one flute, against a delimitingwall of the flute both radially and also tangentially with respect tothe at least one flute, so that a greater gas-tightness of the resultingpositive fit between housing and ceramic base element can be achieved.

A further increase in gas-tightness can also be achieved by heating thehousing, before the second step of pressing the housing in positivelyfitting fashion onto the ceramic base element in the region of the atleast one flute, so that the housing elongates; and by cooling thehousing after the second step so that it contracts and tensile stressesare produced in the housing with respect to the ceramic base element inthe region of the at least one flute. This feature once again enhancesthe hot tightness of the seal that is formed between the ceramic baseelement and the metallic housing. “Hot tightness” is understood here asthe tightness, in particular the gas-tightness, of the sealing apparatusupon heating.

A further advantage lies in the fact that the housing is heated toapproximately 300° C. As a result, all common corrosion protectioncoatings, for example zinc, transparent chromating, or corrosionprotection lacquer, can be applied before assembly of the sealingapparatus and before sealing of the ceramic base element in the metallichousing, without causing those corrosion protection coatings to reachtheir melting point as a result of the heating.

A further advantage lies in the fact that the ceramic base element iscooled during heating of the housing. This increases the temperaturedifference between the housing and the ceramic base element, therebyincreasing, the tensile stresses produced in the housing, after coolingof the housing, with respect to the ceramic base element in the regionof the at least one flute.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the method step essential for the method for sealingaccording to the present invention.

FIG. 2 shows the sealing apparatus according to the present inventionconstituted by such a method.

DETAILED DESCRIPTION

In FIG. 1, 1 designates a sealing apparatus that can be used, forexample, for a spark plug, a sheathed-element glow plug, or a lambdasensor. In the case of the spark plug or sheathed-element glow plug, thesealing apparatus is used in an engine compartment, for example in acylinder head; whereas in the case of a lambda sensor it is used in anexhaust duct. Sealing apparatus 1 encompasses a ceramic base element 5that has, on an outer wall 15, at least one circumferential flute 20. InFIG. 1, sealing apparatus 1 that is to be constituted is shown in alongitudinal section, flutes 20 being implemented in the form ofconstrictions around the circumference of outer wall 15 that reduce thecross-sectional area and the diameter of the cross section of ceramicbase element 5. In a first method step upon assembly of sealingapparatus 1, ceramic base element 5 is introduced or inserted into ametallic housing 10 along a longitudinal axis 45 of housing 10. Ceramicbase element 5 has a sealing seat 40 at which, upon introduction intohousing 10, it makes contact against a sealing ring 50 protruding in theinterior of housing 10.

Ceramic base element 5 lies in housing 10 substantially coaxially withhousing 10 with respect to longitudinal axis 45, as shown in FIG. 1. Inthe region of a bottommost flute 55, facing toward sealing seat 40, ofceramic base element 5, housing 10 has a circumferential outer edge 35.In a second method step, a reduction or drawing ring 30 is placed onthis outer edge 35. The inside diameter of reduction or drawing ring 30proceeds from a value that is less than the diameter of outer edge 35 toa value that is greater than the diameter of outer edge 35. For thisexemplary embodiment, it is to be assumed by way of example that ceramicbase element 5 and housing 10 are disposed in substantially rotationallysymmetrical fashion, and have a cross section of substantially circularor annular shape. When reduction or drawing ring 30 is then placed, withits inside diameter varying as described, on outer edge 35, and ispushed by an application force against outer edge 35 oppositely to theinsertion direction of ceramic base element 5, in the arrow directionlabeled with reference character 55, radial and tangential forces thusact on ceramic base element 5 in the region of flutes 20. The radialforces are directed toward longitudinal axis 45 and thus toward flutes20, and are thus perpendicular to arrow direction 55. The tangentialforces extend tangentially with respect to flutes 20 and thus in arrowdirection 55. In this operation, ceramic base element 5 is pushed intohousing 10 in the insertion direction (which is identified in FIG. 1 byreference character 60 and thus extends oppositely to arrow direction55), and is held in housing 10 in the region of sealing ring 50 andsealing seat 40. Outer edge 35 is part of an elevation 65 on an outerwall 70 of housing 10. Elevation 65 of housing 10 extends substantiallyin the region in which ceramic base element 5, inserted into housing 10,has flutes 20. Reduction or drawing ring 30 is displaced bycorresponding pressure over elevation 65 in arrow direction 55oppositely to insertion direction 60, beginning at outer edge 35, sothat housing 10 is pressed in positively fitting fashion onto ceramicbase element 5 in the region of elevation 65 and thus of flutes 20. As aresult of the variable inside diameter (as described) of reduction ordrawing ring 30, which diameter assumes smaller values even than thediameter of outer edge 35 and thus of elevation 65 as depicted in FIG.1, elevation 65 is reduced to this smallest inside diameter of reductionor drawing ring 30. This is depicted in FIG. 2, in which the positivelyfitting join thus formed between housing 10 and ceramic base element 5after pressing is illustrated by way of reference character 75. In thiscontext, housing 10 conforms to a certain extent, in the region offlutes 20, to the delimiting walls of flutes 20. With suitable pressurefrom reduction or drawing ring 30 upon displacement over elevation 65 inarrow direction 55, the join formed between housing 10 and ceramic baseelement 5 in the region of flutes 20 is also gas-tight, for example to20 bar. The method described for pressing housing 10 onto ceramic baseelement 5 in the region of flutes 20 is a mechanical reshaping method.

As an alternative to the mechanical reshaping method just described,provision can also be made to compress housing 10 at elevation 65 in theradial direction with respect to longitudinal axis 45 (and thus toflutes 20), for example by using round pliers, in order to press housing10 onto ceramic base element 5 in the region of flutes 20. A tangentialforce, as depicted by arrow direction 55 in FIG. 1 for the firstexemplified embodiment, is then not applied in this alternativeembodiment. With appropriate radial pressure, however, a correspondinglygas-tight join can likewise be achieved between housing 10 and ceramicbase element 5 in the region of flutes 20, housing 10 once again, asdepicted in FIG. 2, conforming to a portion of the delimiting walls offlutes 20.

The radial and/or tangential forces described can also, alternatively oradditionally, be achieved by way of a magnetic reshaping method, inwhich a correspondingly strong magnetic field is created in a shortperiod in the region of elevation 65 so that housing 10 is pressed ontoceramic base element 5 in the manner described.

Provision can additionally be made for housing 10 to be heated,especially in the region of elevation 65, before the second method step.As a result, housing 10 is elongated in the direction of longitudinalaxis 45 in the region of elevation 65. The heating of housing 10 can beaccomplished before or after the introduction of ceramic base element 5into housing 10. When housing 10 is then cooled again after the secondmethod step, it thus contracts in the region of elevation 65 so thattensile stresses are produced in housing 10, with respect to ceramicbase element 5, in the region of flutes 20. These tensile stressesenhance the gas-tightness achieved, by way of the magnetic and/ormechanical reshaping method described, in the join between housing 10and ceramic base element 5 as shown in FIG. 2. This effect can also beintensified if ceramic base element 5 is cooled or kept cool during theheating of housing 10. The temperature difference between ceramic baseelement 5 and housing 10 is thus increased, so that the tensile stressesproduced after cooling of housing 10 are further increased. The tensilestresses brought about as a consequence of the heating of housing 10also result in enhanced hot tightness of the sealing apparatus, i.e. anenhanced tightness when the sealing apparatus is operated at hightemperatures, as is the case e.g. with spark plugs, sheathed-elementglow plugs, or lambda sensors.

Advantageously, in order to produce the desired tensile stresses,housing 10 is heated to a temperature that is below the meltingtemperature of common corrosion protection coatings, for example zinc,transparent chromating, or corrosion protection lacquer. Theadvantageous result is that metallic housing 10 can be equipped, beforethe assembly of sealing apparatus 1, with such a corrosion protectioncoating, which then does not melt upon heating of housing 10 to producethe desired tensile stresses and is not thereby destroyed. Heating ofthe metallic housing 10 to approximately 300° C. satisfies therequirement that the desired tensile stresses be produced; thistemperature also lies below the melting temperature of all commoncorrosion protection coatings.

The heating operation just described will be referred to hereinafter as“semi-hot” assembly.

Alternatively or in addition to semi-hot assembly, the gas-tightness ofsealing apparatus 1 constituted by the above-described magnetic ormechanical reshaping operation can also be enhanced by the fact that ina third method step, ceramic base element 5 is at least partiallysoldered to housing 10. This requires the use of a solder that bondsboth to the metallic housing 10 and to ceramic base element 5. This canbe achieved, for example, with a silver solder. Gas-tightness isenhanced in particular, in this context, by the fact that ceramic baseelement 5 is soldered to housing 10 in the region of flutes 20 in whicha seal between ceramic base element 5 and housing 10 has already beenachieved, in the second method step, by way of the above-describedmagnetic and/or mechanical reshaping method and, optionally, by way ofthe above-described semi-hot assembly.

The number of flutes mentioned in ceramic base element 5 can be selectedto be equal to 1 or any number greater than 1.

Ceramic base element 5 can be embodied as an insulator of a spark plug,and in that case is also referred to as a plug insulator. Metallichousing 10 is then, in this case, a plug housing of the spark plug.

Alternatively, however, ceramic base element 5 can also be embodied asthe heating element of a sheathed-element glow plug, the metallichousing 10 then being a plug housing of the sheathed-element glow plug.

Alternatively, however, ceramic base element 5 can also be embodied asthe base element of a lambda sensor, the metallic housing 10 then beinga housing of the lambda sensor.

1-16. (canceled)
 17. A sealing apparatus, comprising: a ceramic baseelement; and a metallic housing, wherein: the ceramic base elementincludes on an outer wall at least one circumferential flute in a regionof which the metallic housing is pressed in positively fitting fashiononto the ceramic base element.
 18. The sealing apparatus as recited inclaim 17, wherein: the sealing apparatus is for one of an enginecompartment and an exhaust duct.
 19. The sealing apparatus as recited inclaim 17, wherein: the ceramic base element is at least partiallysolder-joined to the metallic housing.
 20. The sealing apparatus asrecited in claim 19, wherein: the ceramic base element is solder-joinedto the metallic housing in a region of the at least one circumferentialflute.
 21. The sealing apparatus as recited in claim 17, wherein: theceramic base element includes an insulator of a spark plug, and themetallic housing includes a plug housing of the spark plug.
 22. Thesealing apparatus as recited in claim 17, wherein: the ceramic baseelement includes a heating element of a sheathed-element glow plug, andthe metallic housing includes a plug housing of the sheathed-elementglow plug.
 23. The sealing apparatus as recited in claim 17, wherein:the ceramic base element includes a base element of a lambda sensor, andthe metallic housing includes a housing of the lambda sensor.
 24. Amethod for sealing a ceramic base element in a metallic housing,comprising: inserting the ceramic base element into the metallichousing; and pressing, in a positively fitting fashion, the metallichousing onto the ceramic base element in a region of at least onecircumferential flute disposed on an outer wall of the ceramic baseelement.
 25. The method as recited in claim 24, wherein: the pressing ofthe metallic housing includes pressing on the metallic housing by way ofa magnetic reshaping operation.
 26. The method as recited in claim 24,wherein: the pressing of the metallic housing includes pressing on themetallic housing by way of a mechanical reshaping method.
 27. The methodas recited in claim 26, wherein: the inserting of the ceramic baseelement includes introducing the ceramic base element into the metallichousing substantially coaxially with the metallic housing, and thepressing of the metallic housing includes placing one of a reductionring and a drawing ring on an outer edge of the metallic housing andpushing the one of the reduction ring and the drawing ring radiallytoward the at least circumferential one flute in order to press themetallic housing sealingly onto the ceramic base element in the regionof the at least one circumferential flute.
 28. The method as recited inclaim 27, further comprising: pushing the one of the reduction ring andthe drawing ring tangentially with respect to the at least onecircumferential flute against the outer edge of the metallic housing,while the ceramic base element is held in the metallic housing againstthe tangential force.
 29. The method as recited in claim 24, furthercomprising: before the pressing of the metallic housing, heating themetallic housing in order to elongate the metallic housing; and afterthe pressing of the metallic housing, cooling the metallic housing inorder to contract the metallic housing, thereby producing tensilestresses in the metallic housing with respect to the ceramic baseelement in the region of the at least one circumferential flute.
 30. Themethod as recited in claim 29, wherein: the metallic housing is heatedto approximately 300° C.
 31. The method as recited in claim 29, furthercomprising: during the heating of the metallic housing, cooling theceramic base element.
 32. The method as recited in claim 24, furthercomprising: at least partially solder-joining the ceramic base elementto the metallic housing.
 33. The sealing apparatus as recited in claim32, wherein: the ceramic base element is solder-joined to the metallichousing in the region of the at least one circumferential flute.